United Press International - Saturday, June 26, 1999
Ed Susman, UPI

Dr. John Mellors, professor of medicine at the University of Pittsburgh, said a new study showed that when the genetic tests are performed to determine how the virus in patients has evolved and the patients are treated on the basis of those tests, the viral load decreases greater than when patients are just switched from one drug to another without the tests.

Genetic tests for determining resistance to various AIDS drugs is still considered experimental.

``At least in the short-term,'' Mellors said, ``it appears that resistance testing is better for the patient.''

Mellors, co-chairman of the 3rd International Workshop on HIV Drug Resistance and Treatment Strategies in San Diego, said the study of resistance testing only applied to patients who already were being treated with anti-retroviral medication. Mellors said resistance to medication occurs because the virus has the ability to mutate in different ways so that it can blunt the effects of the drugs.

He said one study found that the virus can reshape itself so that it can reverse the effects of AZT, the oldest drug used against AIDS and still a part of many combination treatments.

Mellors said the resistance testing was most practical in treating people who have been under therapy. Studies presented at the workshop indicated that resistant virus is rarely found among people infected with HIV who have not received medication to fight the infection.

Studies presented in February at an HIV meeting in Chicago suggested that as many as 20 percent of patients were initially infected with resistant forms of the virus. However, at that time Mellors predicted that when the data matured, the percentages would be far lower.

In fact, he said, new data showed that far less than 10 percent of newly infected patients had resistant strains. About 3 percent of new patients turned out to be resistant to the class of drugs known as nucleoside analogs, such as AZT; 3 percent of patients showed resistance to protease inhibitors; about 7 percent were resistant to non-nucleoside analogs, a third class of anti-HIV drugs.

About 200 scientists attended the session, Mellors said, and they also heard data on new drugs making their way to the marketplace, including an Abbott drug, ABT-378, an experimental protease inhibitor.

Mellors said the drug seemed to be effective even among patients for whom another protease inhibitor had failed. He said preliminary reports on other protease inhibitors as well as drugs in other classes also looked promising, but those drugs have not yet been used in clinical trials.

Among these new drugs is a new fusion inhibitor. Fusion inhibitors prevent the virus from attaching to immune cells, preventing invasion of those cells.
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